Many strategies exist for handling various aspects of engine control during engine transients. Examples are found in U.S. Pat. Nos. 6,067,957; 5,778,850; 5,746,183; and 4,932,376. In general, an engine transient strategy involves detection of a transient sufficient to call for some modification of a control parameter, determining an appropriate modification, and then applying the modification to the control parameter.
One form of modification involves the determination of an appropriate adder and application of the adder to the control parameter. The intent is to minimize, and ideally eliminate, the effect of the transient on an engine function controlled by the control parameter during the transient. The ability of processors in engine control systems to rapidly process data in real time enables transients to be quickly detected and suitable modifiers developed and applied.
When an engine is running essentially in a steady-state condition, meaning that engine speed and engine load are both essentially constant, an engine control strategy may provide a particular set-point of operation for a particular control parameter for maintaining operation at that particular set-point. A change in any of several different inputs to the engine may initiate a transient that when concluded, results in engine operation at a new and different set-point. During a transient, the processing of data will continually update the set-point for a sub-system whose inputs are changing because of the transient. The dynamics of the event may be such that a significant disparity is created between the data value calculated for the set-point for a particular control parameter and a data value that would provide a more appropriate value given the nature of the event. Consequently, modification would be appropriate in that instance.
Engine transients have implications on various aspects of engine performance. For example, they may have the potential to cause poor engine response, momentary spikes in certain constituents of tailpipe emissions, momentary engine misfire, and/or undesirable noises. Adjustment of the data values for certain engine control parameters therefore becomes appropriate during engine transients.
One example of an input that can initiate an engine transient is accelerator pedal position. When a driver depresses the accelerator pedal in a vehicle, the engine control system will typically respond by calling for increased fueling. When the driver releases the accelerator pedal, the engine control system will typically respond by calling for decreased fueling. This particular example is driver-initiated, with the input to the engine control system being an on-board signal from a sensor, i.e. an accelerator position sensor.
Another example of an input to the engine that can initiate a transient is a change in engine load. A change in engine load can originate on-board the vehicle, for example when the load imposed on the engine by an engine-driven accessory changes.
The source of a change in engine load can also originate external to the vehicle. For example, if a vehicle that is running on a horizontal road surface at a constant speed with its engine operating in essentially a steady-state condition encounters a headwind or a hill, engine load will increase. If the driver does not operate the accelerator pedal in an attempt to maintain speed, the increased load will initiate a transient because the engine will begin to decelerate. Although the transient that is induced by a change in engine load in this latter example does not originate through driver action or through a change in an on-board sensor, the event will be indicated to the engine control system by change in the value of engine speed data being processed by the control system. As the load increases and the engine and vehicle both begin to slow, the driver may intentionally further depress the accelerator pedal in an attempt to maintain vehicle speed, and in that instance, the change in accelerator pedal position will also be noticed by the engine control system. Engine speed data is derived in any conventional manner and typically published on a data bus serving a processor in the control system.
A typical engine control system may be considered to comprise various control sub-strategies. Heretofore, a control strategy may have handled an engine transient in different ways for different sub-strategies. In other words, a particular transient control strategy might be unique to a particular subsystem. Certain trade-offs or compromises may have had to be made between the various sub-systems in order to meet global engine requirements for a handling a full range of transients and a full range of steady-state operating set-points.
Engine fueling is an example of one such sub-strategy. Within that particular sub-strategy, both the amount of engine fueling and the timing of engine fueling may be controlled.